The present invention relates to the field of mass storage devices. More particularly, this invention relates to fabrication of cylindrical targets used in sputter deposition of storage discs.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
In the disc drive industry, high-performance, thin-film storage discs produced by depositing successive layers on a substrate apparatus for preparation of such storage discs are well known in the art. For storage discs of the type formed on a rigid disc substrate, each layer in the storage disc is deposited in a separate chamber. For example, the under-layer, the magnetic layer, and the over-layer (lubrication layer) are generally deposited in separate processing chambers. Generally, such layers are deposited onto the disc surfaces using sputtering processes.
A typical sputtering system includes a target (a cathode) and a substrate holder (an anode) positioned so that the surface of the substrate upon which the film is to be deposited is placed on the holder, facing the target. Generally the target is a plate material positioned parallel to its respective anodes. Such systems are called planar magnetron sputtering systems. The planar magnetron targets have a number of limitations. Analysis of film composition of films deposited at low pressures has revealed undesirable stoichiometric variations. At high pressures, atomic percentages of certain elements in targets after sputtering at high pressure have not been found to be uniform; that is, the various compounds appear to depart the target leaving certain elements xe2x80x9crichxe2x80x9d in certain areas and those same elements xe2x80x9cpoorxe2x80x9d in other areas. A primary problem is that the center of the target does not sputter. This leads to a buildup of layers of back scattered target species, which subsequently exfoliate causing film defects on the substrate.
Also, the planar sputter processes do not provide sufficient target utilization and film uniformity across a pallet to meet the production goals of lower cost per disc and higher magnetic property (Mrt/Hc) uniformity. To overcome the above described problems with the planar sputtering process, cylindrical cathodes made of alloys such as CoCrPtB for pass-by metal sputtering are used. Cr, Pt, and B are added to Co to control the crystal lattice size and orientation and the grain size. Pass-by sputtering is used to coat large substrate areas uniformly and quickly. By moving the substrate past the sputter target the film uniformity in the direction of travel can be very uniform if the sputter rate is held constant. If the target is long enough to span the other axis of the substrate, the coating over the substrate will be uniform. Further since the substrate can be continuously moved past the target, large areas can be rapidly coated. In this example many discs are robot-loaded into holes of a vertical plate and transported past magnetron sputter sources, which coat both sides of the disc simultaneously.
Generally, cylindrical cathodes are useful for coating substrates of complex shapes. Because, the cylindrical cathodes have uniform wall erosion rate and the object to be coated has an unobstructed view of the cathode surface. The concept of rotating cylindrical cathodes is generally known. In such a device, a cathode target assembly in the form of an elongated, cylindrical tube carries a layer of material applied to its outer surface that is to be sputtered. The target tube is rotated about its longitudinal axis.
However, so far a cylindrical sputter target made of a brittle alloy such as CoCrPtB for a rotary cylindrical cathode has not been feasible because it is generally not economical. This is because it is generally very difficult to machine alloys including chromium. Employing a fabrication process such as plasma spraying the alloy of CoCrPtB does not guarantee less than 1,000 ppm oxygen in the finished product. Oxygen is thought to form compounds in the films, which lead to undesirable shapes or orientation. During the cooling of the casting, many elements freeze sooner than other materials, and this may not result in the desired alloy uniformity. It is relatively easy to form an alloy such as CoCrPtB by mixing the powdered elements in a metal container, sealing it and pressing the container at high temperature to cause the elements to sinter. After sintering, the container is removed and the billet is rolled into sheets for making targets. Though this process can be used to cut discs with a hole in the center large enough to slide over a backing rod or tube material, it cannot be used to make hollow cylinders. Furthermore, this is an expensive process and generally not feasible.
What is needed is an economically feasible technique for fabricating rotary cylindrical cathodes made of a brittle alloy such as CoCrPtB to meet the production goals of lower cost per disc, higher Mrt/Hc uniformity, and to function reliably at typical sputtering power densities and process parameters.
One aspect of the present invention includes fabricating a non-planar sputter target for a rotary cylindrical cathode. According to the method, a cooling tube having a passage within to receive a cooling medium is formed. Then, multiple annular rings including each of the basic metal constituents of a desired alloy are formed. Then the formed annular rings are attached to the cooling tube such that the exposed outer portions of the annular rings provide a homogeneous layer of the desired alloy on a non-planar substrate when used as the rotary cylindrical cathode during sputtering.
Another aspect of the present invention is a rotary cylindrical cathode for a sputter target. The rotary cylindrical cathode comprises a cooling tube having a passage within the cooling tube to receive a cooling medium. The cooling tube further has an outer surface. The rotary cylindrical cathode further has multiple annular rings having inner and outer ring surfaces. The annular rings are made of each of the basic metal constituents of a desired alloy. The annular rings are arranged and disposed over the outer surface of the cooling tube such that outer ring surfaces of the annular rings provide a homogeneous layer of the desired alloy on a non-planar substrate during sputtering.
Advantageously, the technique described above provides an economically feasible rotary cylindrical cathode made of a brittle alloy such as CoCrPtB to meet the production goals of lower cost per disc, and at the same provide a higher Mrt/Hc uniformity in the sputtered alloy layer over the non-planar substrate. Also the technique provides a rotary cylindrical cathode that can function reliably at typical sputtering power densities and process parameters.